The invention relates to stepping motors, particularly those for use in surgically-implanted devices.
Stepping motors have been known for many years. The simplest stepping motor consists of a permanent magnet rotor surrounded by a stator made up of four electromagnets. By selectively energizing the electromagnets, it is possible to turn the rotor in angular "steps" of 90.degree.. Often the rotor has a plurality of permanent magnets, so as to reduce the angular step size. Some stepping motors replace the permanent magnets on the rotor with regions of different magnetic reluctance; in these, known as variable reluctance motors, the rotor turns to the position of minimum reluctance. Still others, known as hybrids, combine reluctance differences with permanent magnets.
Stepping motors have been used in some medical applications. For example, they have been used in medical infusion pumps for delivering precise volumetric dosages of drugs at prescribed time intervals. In all these applications the stepping motor was located outside the patient's body, either in a portable device carried by the patient or in a bedside unit.
Other types of medical devices (e.g., pacemakers) have been implanted in the body. These have typically relied for a power source on batteries implanted along with the device.